Abstract

Epizootic Hemorrhagic Disease Virus (EHDV) is an insect-transmitted pathogen of
ruminants, causing periodic and significant losses in wild and captive deer
populations and less frequently, a bluetongue-like disease in cattle. The serogroup of
EHDV within the Orbivirus genus of the Reoviridae family consists of seven
serotypes, in which emerging serotypes pose an increasing risk either regionally or
globally, due to the insect vectors. To date, no vaccine against EHDV is
commercially available, apart from the live-attenuated vaccine for EHDV-2 (IBAV). In
this study, Virus-Like Particles (VLPs) of EHDV-1 and heterologous VLPs of EHDV-2
were generated using baculovirus multigene expression system for the synthesis of
the two outer and two inner capsid proteins, essential for the formation of VLPs. The
assembly of EHDV-1 recombinant structural proteins into Core-Like particles (CLPs,
two proteins) and (VLPs, four proteins) was confirmed by EM analysis. The biological
activity of the raised antisera to neutralise EHDV-1 was efficiently confirmed by
neutralisation assay at 1:64 dilution. Cross neutralising activities were also detected
against EHDV-2 and EHDV-6 serotypes at 1:8 dilution. Results presented in this
study validate the potential efficacy of the VLP as a neutralising vaccine and strongly
suggest its use as vaccine candidate.
Additionally, an alternative approach was also initiated in this research to develop a
rational vaccine against EHDV-2 using the reverse genetics system (RG). Towards
this, it was first established that in vitro synthesised transcripts from purified EHDV-2
cores could generate infectious virus upon cell transfection. Note that both the
generation of core transcripts and recovery of infectious virus of EHDV were not
demonstrated previously. Subsequently a complete set of 10 T7 transcripts was synthesised, however, it was not possible to recover any infectious virus, likely to be
some unwarranted mutations. Nevertheless, these transcripts will be further
investigated for future RG studies.